Contamination due to foregrounds ( Galactic and Extra-galactic ) , calibration errors and ionospheric effects pose major challenges in detection of the cosmic 21 cm signal in various Epoch of Reionization ( EoR ) experiments .
We present the results of a pilot study of a field centered on 3C196 using LOFAR Low Band ( 56-70 MHz ) observations , where we quantify various wide field and calibration effects such as gain errors , polarized foregrounds , and ionospheric effects .
We observe a ‘ pitchfork ’ structure in the 2D power spectrum of the polarized intensity in delay-baseline space , which leaks into the modes beyond the instrumental horizon ( EoR/CD window ) .
We show that this structure largely arises due to strong instrumental polarization leakage ( \sim 30 \% ) towards Cas A ( \sim 21 kJy at 81 MHz , brightest source in northern sky ) , which is far away from primary field of view .
We measure an extremely small ionospheric diffractive scale ( r _ { \text { diff } } \approx 430 m at 60 MHz ) towards Cas A resembling pure Kolmogorov turbulence compared to r _ { \text { diff } } \sim 3 - 20 km towards zenith at 150 MHz for typical ionospheric conditions .
This is one of the smallest diffractive scales ever measured at these frequencies .
Our work provides insights in understanding the nature of aforementioned effects and mitigating them in future Cosmic Dawn observations ( e.g .
with SKA-low and HERA ) in the same frequency window .